As protein and fat levels did not affect egg production in this Spanish trial, the researchers concluded that brown egg-laying hens do not require more than 16.5 per cent crude protein in the diet. The heavier hens produced more larger eggs than lighter birds but feed efficiency per kilogram of eggs produced was not significantly different.
In a paper published recently in Poultry Science, A. Pérez-Bonilla of Camar Agroalimentaria S.L. and co-authors there and at Universidad Politécnica de Madrid describe a trial they conducted to study the influence of crude protein and fat content of the diet on performance and egg quality traits of brown egg-laying hens from 22 to 50 weeks of age.
The experiment was conducted as a completely randomised design with eight treatments arranged factorially with four diets and two initial bodyweights of the hens (1,592 versus 1,860g). Three of the diets differed in the crude protein content (16.5, 17.5 and 18.5 per cent) and included 1.8 per cent added fat. The fourth diet also had 18.5 per cent crude protein but was supplemented with 3.6 per cent fat instead of 1.8 per cent fat.
Each treatment was replicated four times, and the experimental unit consisted of 21 hens allocated into groups of seven in three adjacent cages. All diets were isocaloric (2,750kcal of AME per kg) and met the recommendations of brown egg-laying hens for digestible arginine, isoleucine, lysine, methionine, threonine, tryptophan, total sulphur amino acids and valine.
Productive performance and egg quality were recorded by replicate every 28 days.
For the entire experimental period, diet did not affect any of the productive performance traits studied but the heavier hens had higher average daily feed intake (120.6 versus 113.9g; P<0.001), egg production (92.5 versus 89.8 per cent; P<0.01), and egg weight (64.9 versus 62.4g; P<0.001) than the lighter hens.
Initial bodyweight did not affect feed conversion per kilogram of eggs or hen mortality but bodyweight gain was higher (289 versus 233g; P<0.01) and feed conversion ratio per dozen of eggs was better (1.52 versus 1.57; P<0.01) for the lighter than for the heavier hens.
None of the egg quality variables studied was affected by dietary treatment or initial bodyweight of the hens.
Pérez-Bonilla concluded that brown egg-laying hens, irrespective of their initial bodyweight, do not need more than 16.5 per cent crude protein to maximise egg production, provided that the diet meets the requirements for key essential amino acids. Heavier hens produce more eggs that are larger than lighter hens but there was no difference in feed efficiency per kilogram of eggs produced.
Pérez-Bonilla A., C. Jabbour, M. Frikha, S. Mirzaie, J. Garcia and G.G. Mateos. 2012. Effect of crude protein and fat content of diet on productive performance and egg quality traits of brown egg-laying hens with different initial body weight. Poult. Sci., 91(6):1400-1405. doi: 10.3382/ps.2011-01917